What made London Samaritan so brave

(CNN) — It’s hard to imagine a scene more gruesome and disturbing than the one Londoners encountered on an inner-city street last Wednesday.

A person hacked to death, lying in a pool of his own blood. His assailants standing nearby, covered in blood and brandishing gore-soaked knives and meat cleavers as they spew violent rhetoric. A car smashed into a lamppost a few yards away.

Most bystanders kept their distance, understandably.

Yet one woman directly confronted the apparent murderers — in fact, she jumped off her bus and rushed to the scene when she saw what looked like a car accident, then stuck around and tried to engage both attackers in conversation even after she realized what was going on. The woman, a 48-year-old mother of two named Ingrid Loyau-Kennett, later said she was trying to talk them down and keep them from hurting anyone else, especially children. Why did she put herself on the line when so many others stayed away?

We don’t really know enough about Loyau-Kennett to be able to say for sure; perhaps we never will. History is filled with heroes, from Oskar Schindler to Paul Rusesabagina of Hotel Rwanda fame, whose life histories couldn’t have predicted the extraordinary things that they later did.

But what we do know, thanks to social psychology, is that what separates people like Loyau-Kennett from the rest of us is often extremely subtle. In fact, research suggests that many of us, perhaps to our own surprise, have the potential to find our own inner hero. What often makes the difference between a bystander and an “upstander” are the particulars of a crisis situation and how those details interact with a person’s background.

For instance, decades of research on the “bystander effect” has shown that even good, moral people fail to take action when confronted with an emergency. One famous study found that the only factor that determined whether bystanders stopped to help someone in need was whether they were in a hurry.